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A307758 Average of twin prime pairs that is a product of two averages of twin prime pairs. 2
72, 108, 180, 240, 432, 600, 828, 1152, 1620, 1872, 2088, 2592, 3528, 3852, 4128, 4932, 4968, 5280, 6300, 6552, 6792, 7488, 7560, 9000, 9240, 9720, 10008, 10332, 11160, 11700, 12240, 13008, 13680, 15288, 16632, 18540, 20232, 20772, 20808, 21492, 25308, 25800, 26892 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms == 0, 24, 36 or 48 (mod 72). - Robert Israel, Apr 30 2019

LINKS

Robert Israel, Table of n, a(n) for n = 1..2451

EXAMPLE

108 = 6*18. 6 and 18 are both averages of twin prime pairs, so 108 is in the sequence.

MAPLE

N:= 10^5: # to get all terms <= N

P:= select(isprime, {seq(i, i=3..N+1, 2)}):

TPA:= map(`+`, P, 1) intersect map(`-`, P, 1):

R:= select(t -> ormap(d -> member(t/d, TPA), TPA intersect numtheory:-divisors(t)), TPA):

sort(convert(R, list)); # Robert Israel, Apr 30 2019

PROG

(PARI) isok1(n) = isprime(n-1) && isprime(n + 1);

isok2(n) = fordiv(n, d, if (isok1(d) && isok1(n/d), return(1)); );

isok(n) = isok1(n) && isok2(n); \\ Michel Marcus, Apr 27 2019

CROSSREFS

Cf. A014574.

Sequence in context: A102562 A216426 A308053 * A272191 A072412 A052486

Adjacent sequences:  A307755 A307756 A307757 * A307759 A307760 A307761

KEYWORD

nonn

AUTHOR

Dmitry Kamenetsky, Apr 26 2019

STATUS

approved

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Last modified May 11 02:34 EDT 2021. Contains 343784 sequences. (Running on oeis4.)